Highback chair



FIG. 1 is a perspective view of a highback chair taken from above and from the right side showing my new design, the chair base and arms shown in chain-dotted lines not being part of the design;

FIG. 2 is a left side view thereof, the right side being a mirror image;

FIG. 3 is a front view thereof;

FIG. 4 is a plan view thereof; and,

FIG. 5 is a rear view thereof. 

The ornamental design for a highback chair, as shown and described. 